1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly, to an apparatus and method of protecting a fuser unit capable of preventing deformation of a fuser unit that may occur during an abnormal operation by monitoring an operation state of the fuser unit, and an image forming apparatus including the apparatus to protect the fuser unit.
2. Description of the Related Art
A fuser unit for an eletrophotographic image forming apparatus, such as a laser beam printer (LBP), a photocopier, and a facsimile, fixes a toner image to a sheet of paper using heat generated by a lamp to which an alternating current (AC) voltage is applied. Thus, in order to maintain a lifetime of a fuser unit or prevent deformation of the fuse unit due to heat, the fuser unit has a built-in temperature sensing element. Furthermore, when the fuser unit operates above a tolerable operating temperature and is determined to be operating abnormally, regardless of control by a software circuit unit, a control circuit forcibly cuts off AC power and current supply, thereby preventing a temperature of the fuser unit from continuously rising and also preventing deformation of the fuser unit.
In a conventional image forming apparatus, under abnormal conditions that cannot be controlled by a control circuit, a hardware protection circuit unit may be additionally provided to cut off AC power applied to a fuser unit to stop a temperature of the fuser unit from rising, thereby preventing or suppressing deformation of the fuser unit.
To achieve this, the conventional image forming apparatus is configured to monitor a temperature detected by a temperature sensor on a surface of a belt within the fuser unit and cause the hard protection circuit to operate when the detected temperature exceeds a preset tolerable temperature.
However, the conventional image forming apparatus may have two problems associated with the protection of the fuser unit. In detail, when the belt in the fuser unit continues to rotate by a motor driving the fuser unit or ceases to rotate, the hardware protection circuit is configured to work if the fuser unit is heated due to abnormal reasons so that the temperature of the fuser unit reaches a preset tolerable temperature. In this case, even if heat generated by a heat source is prevented, latent heat is not uniformly applied to a belt surface, and thus the belt surface may be adversely affected. Another drawback is that a temperature overshoot may occur. More specifically, in order to minimize a First Page Out Time (FPOT), heating characteristics of a lamp/belt/roller within the fuser unit are improved, and a fusing temperature rising speed is increased so that the temperature of the fuser unit reaches a target fusing temperature as fast as possible. However, when the fuser unit is heated to the tolerable temperature and the hardware protection circuit begins to operate, a temperature overshoot may occur even if the heat source is prevented from generating heat. That is, as a fusing temperature rising slope becomes steeper, latent heat applied to the surface of the belt within the fuser unit causes the temperature of the fuser unit to rise above the target temperature before dropping back to the target temperature.
The above two problems may cause a significant overshoot even after preventing release of heat by a heat source with a hardware protection circuit simply having a temperature sensing function. Such a large overshoot will lead to deformation of a belt surface or within a fuser unit.